In a webbing take-up device with which a vehicle is equipped, there is provided a webbing take-up device having so-called webbing sensitive type (WSIR: Webbing Sensitive Inertia Reel) lock means in which, in accordance with a rapid pulling out of a webbing, rotation of a lock wheel is delayed, a take-up shaft and the lock wheel rotate relatively to each other, the lock means operates, the take-up shaft is stopped from rotating in a direction in which the webbing is pulled out, and the webbing is instantaneously prevented from being pulled out.
In this webbing sensitive type webbing take-up device, when an operation of the lock means is canceled, the operation of the lock means is cancelled by rotating the take-up shaft in a small amount in the direction in which the webbing is pulled out.
However, when fastening of the webbing is released by a vehicle occupant, since the take-up shaft is energized by energizing means in the direction in which the webbing is taken up, when the vehicle occupant unfastens the webbing, the webbing may be rapidly taken up. In such a state, when the taking up of the webbing has been completed, the rotation of the take-up shaft is rapidly terminated. The webbing take-up device is thereby in the same state as that when the webbing is rapidly pulled out, and there are cases in which the lock means operates.
In this case, the webbing is set in a state in which the entire amount of the webbing is taken up. There is no longer any allowance for the take-up shaft to rotate in the direction in which the webbing is taken up. Accordingly, there arises a drawback (end lock) in which it becomes difficult to release the lock means.
Therefore, conventionally, there has been proposed a webbing take-up device that solves this drawback (Japanese Patent Application Laid-Open (JP-A) No. 62-95058).
With reference to FIG. 17, a webbing take-up device of this type will be described hereinafter. A lock wheel 306 is rotatably supported at one end portion 304A of a take-up shaft 304 for taking up a webbing 302. A pair of lock plates 312 are disposed at the lock wheel 306. The pair of lock plates 312 mesh with an internally toothed gear 310 which is fixed to a frame 308, and thereby prevents the rotation of a take-up shaft 14. Further, a rotor 314, which rotates integrally with the take-up shaft 304, is connected to the one end portion 304A of the take-up shaft 304. A boss portion 316A of a cam 316 is inserted into the rotor 314. The cam 316 can rotate due to a frictional force between the rotor 314 and the cam 316. This cam 316 is held by a friction spring 320 provided at a cover body 318 by a force that is stronger than the frictional force between the rotor 314 and the cam 316.
A twisting coil spring 322 is disposed between the lock wheel 306 and the rotor 314. The twisting coil spring 322 energizes the lock wheel 306 in the direction in which the webbing is pulled out (the direction of arrow B in FIG. 17).
A protruding portion 324 is formed at the aforementioned lock wheel 306. A pawl 326 which is rotatably supported by a pin 314A of the rotor 314 is able to abut this protruding portion 324.
In the webbing take-up device which is structured as described above, when the webbing is taken up, if the take-up shaft 304 rotates in the direction in which the webbing is taken up (the direction of arrow A in FIG. 17), the rotor 314 rotates integrally with the take-up shaft 304. In this case, the rotational force of the rotor 314 is transmitted to the cam 316 through a predetermined frictional force; however, because the cam 316 is held by the friction spring 320, the cam 316 does not rotate.
Therefore, one end portion 326A of the pawl 326 abuts a notched surface 316B of the cam 316, and the pawl 326 thereby rotates around the pin 314A as a center in the direction of arrow C. Accordingly, the pawl 326 engages with the protruding portion 324 of the lock wheel 306, and thereby prevents the lock wheel 306 and the take-up shaft 304 from rotating relatively with each other.
As a result, when all of the webbing is taken up, since the take-up shaft 304 is not locked by the lock plates 312, the webbing 302 can be pulled out easily.
In a webbing take-up device having such a conventional end lock prevention mechanism as described above, because the cam 316 is solely held by the friction spring 320, when the webbing is rapidly taken up, the cam 316 rotates by the frictional force between the rotor 314 and the cam 316, and end lock is thereby caused.